Abstract
A search is presented for excited quarks of light and heavy flavor that decay to γ+jet final states. The analysis is based on data corresponding to an integrated luminosity of 35.9fb−1 collected by the CMS experiment in proton–proton collisions at s=13TeV at the LHC. A signal would appear as a resonant contribution to the invariant mass spectrum of the γ+jet system, above the background expected from standard model processes. No resonant excess is found, and upper limits are set on the product of the excited quark cross section and its branching fraction as a function of its mass. These are the most stringent limits to date in the γ+jet final state, and exclude excited light quarks with masses below 5.5 TeV and excited b quarks with masses below 1.8 TeV, assuming standard model like coupling strengths.
Highlights
High energy proton-proton collisions resulting in a photon and a jet with large transverse momenta provide a powerful means of searching for new physics
We use the γ + jet invariant mass spectra (Figs. 2, 3), the background parametrization, and the q and b theoretical predictions to set 95% confidence level (CL) upper limits on the production cross section of q and b decaying to qγ and bγ, respectively
The asymptotic approximation is found to be in good agreement with the full CLs approximation over the entire mass range
Summary
High energy proton-proton collisions resulting in a photon and a jet with large transverse momenta (pT) provide a powerful means of searching for new physics. Models involving compositeness [1,2,3] predict excited states of quarks that can be identified by searching for events that contain a photon and a jet from their decays. The quantities fs, f , and f are unknown dimensionless constants that represent the strengths of the excited quark couplings to the standard model (SM) partners Their values are determined by the compositeness dynamics, and are usually assumed to be of order unity. Searches have been performed in different channels [5,6,7,8,9,10,11,12], but no evidence for the existence of excited quarks has yet been found This analysis looks for evidence of qg → q → qγ (where q represents u or d) and bg → b → bγ production by searching for resonances in γ + jet final states.
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